The proposed study is a detailed investigation of the intrinsic organization and afferent-efferent connections of the mammalian dorsal column nuclei of cat in the dorsal and in the lateral funiculi of the spinal cord and that these afferents selectively distribute to nuclear regions which have certain cytoarchitectonic and functional characteristics. The research plan aims at clarifying the functional role of these newly described ascending pathways. For this purpose the following points need to be investigated: a. location of cells of origin of non-primary afferents to the dorsal column nuclei of cat. b. efferent projections of cells in those parts of the dorsal column nuclei of the cat which receive non-primary afferents. c. ultrastructural aspects of synaptic terminals of non-primary afferents. d. whether non-primary afferents to the dorsal column nuclei exist in other mammalian species beside the cat and especially in primates (Rhesus monkey). This neuroanatomical research will be based upon an experimental approach and will employ the use of light- and electron microscopy. The methods used include the Nauta and Fink-Heimer techniques and the retrograde transport of horseradish peroxidase. It is expected that the data from the proposed study will contribute to a new interpretation of the significance of the dorsal column-medial lemniscus system in animals and in man.